feat(ffi): add a client example using Avalonia (#443)

ffi/dotnet/Devolutions.IronRdp.AvaloniaExample/Program.cs

@@ -0,0 +1,38 @@
+using Avalonia;
+using System;
+using System.Diagnostics;
+
+namespace Devolutions.IronRdp.AvaloniaExample;
+
+class Program
+{
+    // Initialization code. Don't use any Avalonia, third-party APIs or any
+    // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
+    // yet and stuff might break.
+    [STAThread]
+    public static void Main(string[] args)
+    {
+        InitializeLogging();
+        try{
+            BuildAvaloniaApp()
+            .StartWithClassicDesktopLifetime(args);
+        }catch(Exception e){
+            Trace.TraceError(e.Message);
+        }
+    }
+
+    // Avalonia configuration, don't remove; also used by visual designer.
+    public static AppBuilder BuildAvaloniaApp()
+        => AppBuilder.Configure<App>()
+            .UsePlatformDetect()
+            .WithInterFont()
+            .LogToTrace();
+
+    public static void InitializeLogging()
+    {
+        Trace.AutoFlush = true;
+        TextWriterTraceListener myListener = new TextWriterTraceListener(System.IO.File.CreateText("AvaloniaExample.log"));
+        Trace.Listeners.Add(myListener);
+    }
+
+}